Doubly-oriented aluminum iron magnetic sheets



Oct. 16, 1962 D. PAvLovlc El'AL 3,

DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1, 1956 3Sheets-Sheet l Fig.l.

Rcillingfition/ Magnetic B Properties O [loo] Od y Mo netic A M zfgr lgic rogerfles Properties A-Cube on Edge or Single Orientation B-Oube onFace or Double Orientation Single and Double Crystal OrientofionsE-Punchinq DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1,1956 Oct. 16, 196 D. PAVLOVlC ETAL 5 Sheets-Sheet 2 d d h M M. m R R m Mu 0 O h. c C s w e .w b m .1. w .m 7% D s O M 0 e F A I 4 2 I o 0 ON m 0m 5". P C D u u u n u u 0 m w m w m P w u 0 00- x uB O O- ::n m

Torque Curves 5.5 7; Al-Fe Magnetic Sheet Hal- Fig.3.

Oct. 16, 19 D. PAVLOVIC El'AL 3,058,8 57

DOUBLY-ORIENTED ALUMINUM IRON MAGNETIC SHEETS Filed Aug. 1, 1956 3Sheets-Sheet. 3

Fig.5.

0 Calculated-Doubly Oriented-Cube on Face .2 n Calculated-singlyOriented-cube on Edge E A Actual-singly Oriented-Cube on Edge xActual-Unoriented 0'408'0'1'20'1'60'2'00'2'40 Magnetizing Force OerstedsIntegrated Magnetization Curves far singly an Doubly Oriented MagneticSheet Fig.6.

Fig.4.

' Torque Curves n 2.4%Al-Fe o Doubly Oriented n 6 m l E 0 C o l8 0 45 90l35 l80 Degrees tram Flg Rolling Direction Torque per Volume WITNESSES v\NVENTQRS Q Dusan Pavlovic Karl Foster W 8 John A. Osborn United StatesPatent DQUBLZ This invention relates to doubly-oriented aluminum ironmagnetic sheets and processes for producing them.

It has long been desirable to have available magnetic sheet materialthat is doubly oriented, that is, the crystals or grains of the alloyhave a cube on face orientation in the plane of the sheet that theoptimum magnetic properties extend in two directions substantially atright angles to each other in the plane of the sheet. Further it isdesirable that the optimum magnetic properties in these two directionsshould be approximately equal. Such doubly oriented sheet material wouldhave important practical applications in the electrical industry in themanufacture of electrical motors, generators, transformers and numerousother varieties of electrical devices.

It has been proposed heretofore to produce magnetic sheets from aluminumiron alloys. In particular, in Patent 2,300,336 there is disclosed aprocess for producing sheets of magnetic aluminum iron alloy wherein thealloy is oriented to some extent. However, not only are the kinds oforientation present in doubt, but the extent of desired orientation andthe magnetic properties are relatively low such that the products setforth in this patent have not been as satisfactory as, nor comparablewith available silicon iron alloy magnetic sheets, for example. Singlyoriented silicon iron magnetic sheets are so far superior to themagnetic aluminum-iron sheet available heretofore that suchaluminum-iron magnetic sheets has not been competitive therewith.

The object of the present invention is to provide a process forproducing doubly oriented aluminum-iron alloy magnetic sheets havinggreatly improved optimum magnetic properties in two directions in theplane of the sheet.

A further object of the invention is to provide a process for producingmagnetic sheets from aluminum iron alloys by initially hot rolling abillet or ingot of the alloy to a plate of substantial thickness andthen cold rolling the plate twice to apply a cold reduction of 60% to90% each time, with an intermediate anneal and a final anneal.

A still further object of the invention is to provide a doubly orientedmagnetic sheet of aluminum iron alloy produced by a double cold rollingprocess having substantially similar optimum magnetic properties in twodirections at right angles to each other.

Other object of the invention will in part be obvious and will in partappear hereinafter.

For a better understanding of the nature and objects of the invention,reference should be had to the following detailed drawings anddescription, in which:

FiGURE 1 is a perspective view of a sheet with single and doubleoriented crystals therein;

FIG. 2 is a graph with curves showing the variation in permeability ofsingle and double cold rolled aluminum iron for various angles withrespect to the rolling direction;

FIG. 3 is a graph with torque curves of specimens of single and doublecold rolled 3.5% aluminum iron alloy;

FIG. 4 is a graph with a torque curve of double cold rolled 2.4%aluminum iron alloy;

FIG. 5 is a graph with curves of the integrated magnetic properties forvarious magnetic sheets;

3,058,857 Patented Oct. 16, 1962 FIG. 6 is a plan view of a statorpunching;

FIG. 7 is a plan view of segmental punchings;

FIG. 8 is a plan view of an L-punching; and

FIG. 9 is a plan view of an E-punching.

In accordance with the present invention, it has been discovered thatmagnetic sheets having double crystal orientation may be produced fromaluminum-iron alloys comprising from 1% to 10% by weight of aluminum,and the balance being iron, except for incidental impurities. FIG. 1illustrates the differences in the magnetic characteristics based on thecrystals making up the grains of magnetic sheet where a single anddouble orientation, respectively, has been obtained. It is Well knownfor cubic crystals of alloys of this range of proportions of aluminum iniron that magnetic properties in this cube edge direction are optimum.Permeability in other directions of the crystal, such as the [110]direction, that is, on a diagonal across a cube face, is low compared tothat in the cube edge or [100] direction. A in FIG. 1 indicates that thecubic crystals making up the grains in a singly oriented material haveonly one of the edges of the cube located in the rolling direction. Adoubly oriented grain as shown in B of FIG. 1 has two cube edges lyingin the plane of the sheet so that there are two directions perpendicularto one another within the plane of the sheet which give optimum magneticproperties.

Magnetic sheets having double crystal orientation such that two cubeedges lie in the plane of the sheet may be produced from the aluminumiron alloys comprising from 1% to 10% by weight of aluminum and thebalance being iron except for incidental impurities, by a processcomprising: (1) initially hot rolling of an aluminum iron ingot orbillet to a thickness of the order of from 0.25 to 0.6 inch, (2) coldrolling the plate to effect a reduction in thickness of 60% to (3)annealing the resulting cold rolled sheet for a period of time at atemperature to remove stresses and recrystallize the 'metal, (4) againcold rolling the sheet to ellect a second reduction in thickness of from60% to 90% to produce a sheet having the desired gauge of the order of0.03 inch and less, and (5) finally annealing the sheet fora specifiedtime and temperature. By this process there results a doubly orientedmagnetic sheet wherein a high proportion of the grains have a cube onface orientation in the plane of the sheet. The best results areobtained for compositions comprising 2% to 8% of aluminum. The optimummagnetic properties are secured most regularly if the reduction duringeach cold rolling is at least 70% in steps (2) and (4).

More specifically, aluminum iron alloys for the practice of the presentinvention are prepared from ingots, billets or slabs of an alloy from 1%to 10% aluminum, the balance being iron, except for incidentalcomponents and impurities. The incidental impurities preferably shouldnot exceed 0.01% carbon, and sulphur and phosphorus are usually presentin amounts of less than 0.005%, and only small amounts of oxygen andnitrogen are present in the alloy. There may be present small amounts ofcomponents such as silicon in amounts of the order of 0.01 to 0.05%, andmanganese in amounts of the order of 0.01%. Other elements may bepresent in small amounts.

The alloy may be prepared by melting in an electric furnace under vacuumor in air, the desired proportions of relatively pure iron and aluminum.Good results have been obtained from the alloys melted in an open airinduction furnace. Attention should be directed to insuringsubstantially uniform admixture of the aluminum with the iron. In someinstances a melt of relatively pure iron may be prepared by an oxygenpurification treatment as set forth in US. Patents 2,741,554 and2,741,555 and to the molten iron there is added the pure aluminum in the3 required proportions, usually in a second crucible under a protectiveatmosphere, with appropriate measures taken to assure a thoroughadmixture of the aluminum into the relatively pure iron.

In making sheets, the aluminum-iron ingots or heavy billets or forgedslabs of the alloy in the desired composition, are heated to atemperature of the order of from 800 C. to 1 100 C. and hot rolled orhot forged to produce a plate of a thickness of from 0.25 inch to 0.6inch thickness. The plate may be of any suitable width.

The hot rolled plate is cooled to substantially room temperature, belowat least 600 C. and preferably below 100" C., and then is drasticallycold rolled to effect a reduction in thickness of from 60% to 90%. For aplate of about 0.5 to 0.6 inch in thickness the reduction in thicknesswill be greater, that is, about 90%, while when working with the thinnerhot rolled plate the reduction in thickness will be of the order of 70%;As a result of this first cold rolling there will be produced arelatively thick cold rolled sheet which is then annealed at atemperature of from 700 C. to 1050 C. for at least fifteen minutes inorder to remove stresses and to recrystallize the metal. Longerannealing times may be employed and good success has been had withannealing times of one hour at 1000 C. It has proven to be undesirableto anneal at a temperature of 1100 C. or higher after this initial coldrolling since the recrystallization does not proceed in a satisfactorymanner. In particular, excessive grain size results at excessivetemperatures. The magnetic product after this first cold rolling andannealing is not particularly satisfactory for use in electricalapparatus.

The annealed sheet is then cooled to substantially room temperature andsubjected to further severe cold rolling to effect a second reduction inthickness of from 60% to 90% to produce a sheet of a thickness to meetthe requirements of the particular electrical device to be madetherefrom. Ordinarily, the sheet will be of a'thickness of not in excessof 0.03 inch. During the second cold rolling the crystal structureresulting from the first anneal is effectively changed. It is thecrystal structure after the second cold rolling, which is not presentafter the first cold rolling step, that is necessary for the developmentof a structure orientation during the final anneal.

The thin cold rolled sheet produced by the second cold rolling is thensubjected to a second anneal at a temperature of from 900 C. to 1050 C.for a period of time of at least one hour. The annealing may be appliedto the sheets for as long as 12 hours at 1000 C. without detriment.However, if the annealing temperature is 1100 C. or higher, amagnetically inferior product results. This second anneal results in adiiferent texture than was present in the sheet after the firstannealing treatment. A 'very high proportion of all of the crystals orgrains of the sheet after the second anneal now have a cube on faceorientation in the plane of the sheet. Tests have indicated that theedges of the cube are oriented substantially both in the direction ofthe rolling and in a direction perpendicular to the rolling direction inthe face of the sheet. Consequently, the crystals are oriented to havetheir optimum magnetic properties in the direction of the rolling and inthe direction of right angles thereto. V

In order to provide for the optimum magnetic properties, it is necessaryto conduct the second anneal for a time and temperature such that theaverage grain diameter does not exceed approximately one millimeter.Good results are obtained where the average grain diameter is from 0J1to 0.5 millimeter.

The annealing is preferably carried out in a hydrogen atmosphere inorder to reduce oxides and remove carbon. In some cases the atmospheremay comprise an. inert gas, such as argon, alone, or admixed withhydrogen. The gases should be of a low dew-point, for example 20 C. andlower.

The resulting magnetic sheets after the final anneal will 4 be of athickness of from about 0.03 inch to 0.005 inch and thinner. For use inelectrical motors and generators, particularly desirable sheetthicknesses are from 0.03 inch to 0.02 inch. For some purposes sheets ofa thickness of 0.04 inch are required.

The aluminum iron alloy magnetic sheets produced by the double coldrolling and double annealing treatment of the present invention exhibitsubstantially higher magnetic properties in the two directions alongwhich preferred orientation takes place as compared to sheets otherwisesimilarly produced by a single cold rolling and annealing process.Referring to FIG. 2 of the drawings, there is illustrated thepermeability at 10 oersteds for 2.4% aluminum iron magnetic sheets. Thesheet from which the data of curve A were obtained was produced by hotrolling the aluminum iron ingot to a plate of a thickness of one-halfinch which was then cold rolled twice, effecting areduction of eachtime, the final sheets having a thickness of 0.025 inch, with an annealat '1000 C. for one hour being applied after the first cold rollingoperation and then following the second cold rolling by a two houranneal at 1000 C. The sheet used in the test indicated by curve B wasprepared by hot rolling 2.4% aluminum iron to a thickness of one-eighthinch followed by a single cold roll to produce a sheet of a thickness of0.025 inch which was then annealed at 1000 C. for two hours. Both coldrolled sheets were of a width of approximately 13 inches and Epsteinstrips were cut from the sheet at varying angles with respect to therolling direction. The Epstein strips were annealed in dry hydrogen at1000 C. for two hours before being tested magnetically.

It will be observed from the curves in FIG. 2 that the double coldrolled aluminum iron has a permeability at 10 oersteds approximately 50greater at both the 0 and orientation as compared to the single coldrolled sheet. This difference in permeability in the zero and 90directions is a substantial improvement and quite meaningful in theapplication thereof in electrical devices. The dip in permeability at 45orientation is meaningful, for if there is little change in permeabilityas the direction of flux tothe sheet changes, there is little crystalorientation. It necessarily follows that an increase in doubleorientation will bring about a dip in permeability at the 45 anglerelative to that at 0 or 90.

Torque curves were prepared by testing identically sized samples ofsingle cold rolled and double cold rolled aluminum iron alloy. FIG. 3 isa plot of torque curves for single and double cold rolled 3.5% aluminumiron alloy. FIG. 4 is the curve for double cold rolled 2.4% aluminumalloy. In FIG. 3 the four torque peaks are substantially greater for thedouble cold rolled aluminum iron as compared to the single cold rolledaluminum iron. Furthermore, the differences between the successive peaktorque values are less, both numerically and percentagewise, for thedouble rolled aluminum iron alloy than for the single cold rolledaluminum iron alloy. It is desirable for use in the electrical apparatusthat the torque peaks be reasonably equal for best results. It will benoted that the differences between the torque peaks are of the order of13% for the double cold rolled alloy and over 20% for the single coldrolledv alloy.

The following examples are illustrative of the invention: i

7 Example I There was melted in a vacuum furnace electrolytic iron andaluminum bar of a purity of 99.9%, the aluminum being introduced toprovide approximately 3% by weight of aluminum in iron. During themelting the iron was introduced first into the crucible and was purifiedby passing thereover a stream of wet hydrogen and then dry hydrogen inorder to reduce the carbon and oxygen content. The aluminum was addedunder an argon an 80% The sheet specimens were then annealed two hoursat 15,000 gausses.

atmosphere. The melt was cast into a vertical steel mold to produce aningot of the alloy. The ingot was heated to a temperature ofapproximately 1000 C. and

'was hot rolled to provide a plate of a thickness of onehalf inch. Thehot rolled plate was annealed in a hydrogen atmosphere for one ing theplate to room temperature, it was cold rolled to efiect a reduction of80%. The resulting thick sheet was cut into a number of specimens. Thethick sheet specimens were heat treated at different temperatures, someat 700 C., others at 1000 C. and still others at 1200" C. forone hour.Dry hydrogen of a -50 C. dew-point was used as the annealing atmosphere.The annealed specimens were then given a second cold rolling to efiectreduction to a final thickness of 0.025 inch.

1000 C. in hydrogen. Hollow square members were punched from each of thesheets and annealed one hour at 1000 C. The specimens annealed at 700-C. after the first cold rolling had an induction at 10 oersteds of14,700 gausses. Hollow square members from the sheets annealedat 1000 C.had an induction at 10 oersteds of The hollow square members which hadbeen subjected .to 1200 C. for the first anneal had an induction of14,200 gausses at 10 oersteds. The first anneal at 1200? C. had resultedin a very large grain size in the one-eighth inch thick sheet.

Example 11 i .In another series of tests on a 3% iron aluminum alloy,produced as in Example I, the annealing temperature after the first coldrolling operation was 1000 C. for one hour. The specimens were thenuniformly cold rolled to 0.025 inch and then annealed for one hour attemperatures of 1000 C. for one group, at 1100 C. for a second group,and at 1250 C. for a third group. The average grain diameter for themembers annealed at 1000 C. was approximately 0.1 millimeter and theinduction at 10 oersteds was 14,700. The samples annealed at 1100 C. and1250 C. had an average grain diameter in excess of one millimeter andthe induction was 14,200 and 14,100 gausses, respectively, in a field of10 oersteds.

Example 111 Double cold rolled sheets of a thickness of 0.025 inchproduced from 0.5 inch thick hot rolled plates containing 2.4% and 3.5%aluminum iron, respectively, were prepared by following the procedure ofExample I. The sheets, after being annealed at 1000 C. for one hour inhydrogen following the second cold rolling, were tested to determinetheir magnetic properties. The 2.4% aluminum iron alloy sheets had aninduction of 15,200 gausses at 10 oersteds. :For comparison, a singlecold rolled sheet of the same alloy and of the same thickness had aninduction of 14,500 gausses. The double cold rolled 3.5% aluminum alloywhen tested as Epstein samples had an induction of 16,200 gausses at 10oersteds. All of these specimens showed a high magnetic induction in theplane of the sheet both in the rolling direction and in a direction 90to the rolling direction.

The double cold rolled, doubly oriented aluminum iron magnetic sheets ofthe present invention are particularly well suited for the making oflaminations for motors and generators. The permeability in twodirections at right angles will enable a substantial increase in themagnetic flux density in the laminations.

Referring to FIG. of the drawings, there is illustrated curves plottingthe induction in kilogausses for varying magnetizing forces forunoriented, singly oriented and doubly oriented material. The two uppercurves comprise theoretical calculations. All of the curves areintegrated values. It will be noted that the topmost curves, calculatedfor double oriented material, shows a much greater induction for allmagnetizing fields up to 250 oersteds than does the curve immediatelybelow it hour at 1000 C. After coolwhich is calculated for singleoriented or cube on edge magnetic material. Actual tests have been madeof a number of samples of singly oriented magnetic sheets and it will beobserved that the curve for such singly oriented material approaches thecalculated curve at approximately oersteds. It is evident that theactual values obtained by using unoriented or hot rolled magnetic sheet,shown in the lowest curve, is, for all practical purposes, substantiallythe same as the singly oriented material. At all levels of appliedmagnetizing field, it is seen that the magnetic induction is much higherfor the doubly oriented material than the singly oriented material.

The curve of FIG. 5 illustrates the improvement which may be obtained byusing the doubly oriented material of the present invention forlaminations of dynamoelectric machines such as motors and generators inwhich the magnetic flux must travel in all directions with respect tothe rolling direction. Motor and generator laminations comprising acomplete ring punched from a single sheet of the double orientedmaterial will exhibit the improvement in magnetic properties over singlyoriented material in the same manner as the uppermost curve of FIG. 5excels the lower curves.

tooth and then flows in a transverse direction along the arcuate edge16. The double orientation is indicated at 18. For rotors the teeth willproject radially outwardly from. a central portion. The average magneticproperties of a doubly oriented stator or rotor punchings willcorrespond to the top curve of FIG. 5.

For large electrical motors and generators the laminations are punchedas segments or sectors as illustrated in FIG. 7. The magnetic sheet 20,having double orientation as shown in direction 22 along the length ofthe sheet and direction 23 transverse thereto, is punched to provide aseries of magnetic segments 24 in which the teeth 26 are essentiallyparallel to the one preferred orientation 22 along the length of thesheet 20. Slots 28 are present between the teeth to receive coilstherein. An arcuate edge 30 on each segment 24 is essentially parallelto the other preferred orientation 23. Magnetic flux developed in eachof the teeth 26 travels in the one direction 22 of easiestmagnetization, and then passes along the arcuate edge 30 also in theother direction 23 of easiest magnetization. The magnetic segments 24 ofFIG. 7 will exhibit properties superior to those indicated in the topcurve of FIG. 5. An assembled motor or generator comprising thelamination segments of FIG. 7 will possess outstanding characteristics.

In static induction devices, such as transformers and magneticamplifiers, the double oriented magnetic sheets may be cut or punchedinto various shaped laminations to take advantage of suchcharacteristics. In such laminations there are at least two linearlyextending portions at right angles to each other, parallel to or in linewith the two directions of preferred orientation of the magneticmaterial. In FIG. 8 is shown an L-punching 40 comprising one leg 42 andanother leg 44 at right angles thereto. The L-punching 40 is so cut froma sheet of the doubly oriented aluminum-iron material of the presentinvention that one preferred orientation 46 is parallel to leg 42 whilethe other preferred direction 48 of orientation is parallel to leg 44.Transformers and other electrical devices built from the L-punchings 40will exhibit outstanding magnetic properties.

Referring to FIG. 9, there is illustrated an E-punching 50, comprising aside 52 from which projects lengths 54, 56 and 58 at right anglesthereto. The punching 50 is so made with respect to a sheet of doublyoriented aluminum-iron that one preferred direction 60 of orientation isparallel to side 52, and the other preferred direction 62 of orientationis parallel to the lengths 54, 56 and 58. Such laminations will giveoptimum magnetic cores.

It will be understood that the above description and drawings areexemplary and not limiting.

We claim as our invention:

1. In the process of producing sheets of aluminumiron' alloy comprisingessentially from 1% to by Weight of aluminum and the 'balance being ironexcept for incidental impurities, the grains of the sheet beingpreferentially oriented so that the sheet exhibits optimum magneticproperties in two directions in the plane of the sheet, the stepscomprising hot working a 'body of the aluminum-iron alloy at atemperature of the order of from 800 C. to 1100" C. to produce a plateof a thickness of the order of from 0.25 to 0.6 inch, cold rolling theplate to elfect a reduction in thickness of from 60% to 90%, annealingthe resulting relatively thick sheet at a temperature of from 700 C. to1050 C. [for at least minutes to remove stresses and to recrystallizethe metal, cold rolling the thick sheet to elfect a second and finalreduction in thickness of the order of from 60% to 90% so as to producea thin sheet of a thickness of the order of 0.03 inch and less, andannealing the thin sheet in a reducing atmosphere at a temperature offrom 900 C. 'to 1050 C. for at least one hour to recrystallize the alloyto cube on face grains, which grains have an average diameter notexceeding one millimeter.

2. 'In the process of producing a sheet of an alloy comprisingessentially from 2% to 8% by weight of aluminum and the balance beingiron except :for incidental impurities, the grains of the sheet beingpreferentially oriented so that the sheet exhibits optimum magneticproperties in two directions substantially at right angles to each otherin the plane of the sheet, the steps comprising hot rolling an ingot ofthe aluminum iron alloy at a temperature of the order of from 900 C. to31100" C. to produce a plate of a thickness of approximately 0.5 inccold rolling the plate to effect a reduction in thickness of from toannealing the resulting relatively thick sheet in hydrogen at atemperature of from 900 C. to 1050 C. for a period of time of about onehour, cold rolling the thick sheet a second and final time to efifect afurther reduction of from 60% to 90% to produce a thin sheet of athickness of not in excess of about 0.040 inch, and annealing the thinsheet in hydrogen at a temperature of from 900 C. to 1050 C. for aperiod of at least one hour to recrystallize the alloy to produce cubeon face grains not coarser than an average of 1 mm. diameter.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Bozorth: Ferromagnetism, 1951, D. Van Nostrand Co., Inc.,pages 210 to 220, especially 2117 and 2:18.

1. IN THE PROCES OF PRODUCING SHEETS OF ALUMINUMIRON ALLOY COMPRISINGESSENTIALLY FROM 1% TO 10% BY WEIGHT OF ALUMINUM AND THE BALANCE BEINGIRON EXCEPT FOR INCIDENTAL IMPURITIES, THE GRAINS OF THE SHEET BEINGPREFERENTIALLY ORIENTED SO THAT THE SHEET EXHIBITS OPTIMUM MAGNETICPROPERTIES IN TWO DIRECTIONS IN THE PLANE OF THE SHEET, THE STEPSCOMPRISING HOT WORKING A BODY OF THE ALUMINUM-IRON ALLOY AT ATEMPERATURE OF THE ORDER OF FROM 800*C. TO 1100*C. TO PRODUCE A PLATE OFA THICKNESS OF THE ORDER OF FROM 0.25 TO 0.6 INCH, COLD ROLLING THEPLATE TO EFFECT A REDUCTION IN THICKNESS OF FROM 60% TO 90%, ANNEALINGTHE RESULTING RELATIVELY THICK SHEET AT A TEMPERATURE OF FROM 700*C. TO1050*C FOR AT LEAST 15 MINUTES TO REMOVE STRESSES AND TO RECRYSTALLIZETHE METAL, COLD ROLLING THE THICK SHEET TO EFFECT A SECOND AND FINALREDUCTION IN THICKNESS OF THE ORDER OF FROM 60% TO 90% SO AS TO PRODUCEA THIN SHEET OF A THICKNESS OF THE ORDER OF 0.03 INCH AND LESS, ANDANNEALING THE THIN SHEET IN A REDUCTING ATMOSPHERE AT A TEMPERATURE OFFROM 900% C. TO 1050* C. FOR AT LEAST ONE HOUR TO RECRYSTALLIZE THEALLOY TO CUBE ON FACE GRAINS, WHICH GRAINS HAVING AN AVERAGE DIAMETERNOT EXCEEDING ONE MILLIMETER.